1. Field of the Invention
The present invention relates to a color image printing device for use in, for example, color printers, color copying machines, and color facsimile machines, and more particularly to a color image printing device constructed of a plurality of print engines which transfer toner images of corresponding colors one over the other to a print medium transported on a transporting device.
2. Description of the Related Art
Conventionally, a tandem type color image printer has been known where print engines of yellow, magenta, cyan, and black toner images are aligned along a transport path and the toner images are formed on corresponding photoconductive drums and transferred to a print medium one image over the other in register.
With this type of color image printing device, the print engines are spaced apart so that the print medium is be transported from one print engine to another. This is advantageous over a single photoconductive drum type color printer where the print medium have to be moved back and forth through the single photoconductive drum to transfer the toner images of the respective colors. Therefore, the tandem type printer improves printing speed. In addition, the transfer belt forms a flat, straight transport path, allowing transferring toner images to a thick print medium.
However, the aforementioned conventional color image recording devices suffer from the problem that the photoconductive drums are always in contact with the transport belt directly or with the print medium between the photoconductive drum and the transport belt and therefore the photoconductive drum and transport belt are subjected to wear.
In addition, even when only black toner image is to be printed, all of the print engines are driven. Therefore, toners not actually printed are subjected to mechanical stress. Such a mechanical stress results in shorter usable life of the toner.
An object of the invention is to provide a color printing apparatus where wear and tear of the photoconductive drum and transport belt are minimized.
Another object of the invention is to provide a color printing apparatus where toners are not subjected to excess mechanical stress.
A color image printing apparatus has a plurality of image forming sections with corresponding photoconductive drums on which images of different colors are formed. Each photoconductive drum has formed an image of a corresponding color of print data thereon. The images of the respective colors are then transferred onto print paper in register to form a color image.
Each of a plurality of positioning mechanisms selectively positions a corresponding photoconductive drum at an operative position and a non-operative position. A controlling section controls the positioning mechanism to switch the corresponding photoconductive drum between the operative position and the non-operative position. A color detecting section detects a color in each color plane of a page of the print data. When all of the plurality of positioning mechanisms have been brought to the non-operative positions, the controlling section selectively controls the positioning mechanisms in a first operation mode or in a second operation mode according to the color detected in the color plane by the color detecting section.
The first operation mode is a mode where when the color detecting section has detected a color in each color plane of a first page, the controlling section causes a positioning mechanism corresponding to the color detected by the color detecting section to the operative position, and when the color detecting section has detected a color in a page after the first page which corresponds to a photoconductive drum at the non-operative position, the controlling section causes the positioning mechanism of the photoconductive drum corresponding to the color detected by the color detecting section in the page after the first page to the operative position.
The first operation mode is a mode where if the color detecting section has detected black in each color plane of a first page, the controlling section causes a positioning mechanism to bring a photoconductive drum corresponding to black to bring to the operative position, if the color detecting section has detected any one of yellow, magenta, and cyan black in each color plane of a first page, the controlling section causes all of the positioning mechanisms to the operative positions.
The color image printing apparatus may include a counter which counts a number of times the color detecting section detects in successive pages that all colors in a preceding page are found in a following page. When the counter has counted up to the predetermined value, the controlling section causes positioning mechanisms to bring corresponding photoconductive drums to operative positions, the photoconductive drums corresponding to colors detected by the color detecting section.
The print data may be compressed and compared with compressed reference data so the color plane detecting section can detect respective colors at high speed.
The data converting section may output the bit map data simultaneously to the data detecting section and the data compressing section so that the data compressing section and the data detecting section concurrently operates, thereby increasing the throughput of the printer.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.